Chromatography Forum

Well maybe this is a very stupid question but can someone explain to me step by step how to adjust a split ratio on a hp 5890 seriesII without EPC. I have three valves to adust: column head preassure, total flow and purge valve, and a bubble flowmeter. I need a flow of 20ml/min and a split of 1:20. Please help!!!!!

20 mL/min.? Are you using a packed column? At 20 mL/min. column flow your split flow would have to be 400 mL/min. Split injection is not normally used with packed columns.

No I´m using a normal HP-5 MS column 30m/0,25mm the total flow should be 20 ml/min. In my opinion with a split of 1:20 the column flow should be 1ml/min. Correct me if I´m wrong.

Now I understand. First of all, the total flow must be opened so that there is enough flow to set the column pressure and the purge flow. The column flow is set by adjusting the column head pressure at the operating temperature of the column. Measute the flow through the detector with all other flows shut off. I assume by purge flow you are referring to the septum purge valve. This should be set at 1-2 mL/min measured at the purge vent outlet below the purge valve. Finally, adjust the total flow to 20 mL/min. at the total flow outlet below the total flow valve. I hope there instructions are clear enough.

Use HP Flow Calculator software http://www.chem.agilent.com/cag/servsup ... s/GCFC.htm to determine what head pressure you need to get your desired flow rate through the capillary (enter in your dimensions, temperature, etc.).
Then temporarily open up the total flow valve , maybe halfway. Then set the column head pressure to the desired psi. Now, you know the column flow from the calculator since you know the head pressure and temperature. Measure the flow through the purge vent to get split flow, can calculate split ratio from column flow and the total of column + purge vent flows; adjust the purge flow using the total flow knob until it is at the dired flow rate (adjust the head pressure knob a little if necessary to maintain the desired head pressure). Obviously if the total flow valve is set too low, there will not be sufficient carrier gas available, and if it's too high, then the purge flow will be higher.

"I have three valves to adust: column head preassure, total flow and purge valve, and a bubble flowmeter. I need a flow of 20ml/min and a split of 1:20. Please help!!!!!"

Thanx for your help, I think I have figured it out